In a production of semiconductor devices utilizing silicon (Si), which is the most popular semiconductor material at present, generally, after adding an impurity in Si by an ion implantation and the like method, the Si is heated to 900.degree. C. to 1100.degree. C. with the use of an electrical furnace, a flash lamp annealer, and the like, to activate the impurity in the Si.
In recent years, a semiconductor device utilizing silicon carbide (SiC) has drawn considerable attention in the industry since such a device is excellent in electric power characteristics (high breakdown voltage and high current-carrying capacity), high-frequency characteristics, and resistance in an environment of use. However, the ion implantation and activation of SiC involve many difficulties in comparison with those of Si. In order to overcome such difficulties, several techniques in the impurity activation have been suggested. An example of such techniques is that an impurity is added when forming an SiC film, an ion implantation is carried out under a high temperature of about 500.degree. C. to 1000.degree. C., and thereafter, as disclosed in T. Kimoto, et al., Journal of Electronic Materials, Vol. 25, No. 5, (1996) pp. 879-884 etc., an impurity is activated by a heat treatment at a high temperature of 1400.degree. C. to 1600.degree. C.
However, such methods of impurity activation by a heat treatment requires a step of heating Si and the like semiconductor material with the use of electrical furnace and the like. Consequently, a relatively long time is necessary for the activation, and therefore it is rendered difficult to increase the productivity. Such drawbacks become more conspicuous in the case of using SiC since a further higher temperature is required in the heat treatment. Moreover, in the case of SiC, regarding a p-type dopant, it is difficult to form a semiconductor layer in which the p-type dopant element is activated to a high degree.
In view of such drawbacks, for example, Japanese Unexamined Patent Publication No. 7-022311 discloses such a method of an impurity activation as described in the following. According to this, a laser annealing is conducted by irradiating with a laser light an amorphous Si film in which concentrations of carbon, nitrogen, and oxygen are made to be lower than certain values, in order to form a mixed region in which an amorphous region and a solid-phase ordered region are present together without fusing the amorphous Si film. Then, impurity ions are implanted into the amorphous Si film, and thereafter laser annealing is carried out by irradiating the Si film with a laser light having a wavelength of 248 nm to make an impurity region to be a semi-amorphous state. However, although it is disclosed in the Publication No. 7-022311 that a carrier mobility can be improved by the method when compared with an amorphous Si, a laser annealing for the semiconductors other than the amorphous Si is not mentioned.
A laser light conventionally used for a laser annealing for such a crystallization (activation) of a semiconductor has been a laser light having a wavelength shorter than a wavelength causing a band edge absorption, such as an excimer laser, as described specifically in Y. Morita, et al., Jpn. J Appl. Phys., Vol. 2, No. 2, (1989) pp. L309-L311. In the case of using a laser light having such a wavelength, electrons in the atoms constituting a semiconductor are excited and ionized by the energy of the laser light, and part of the energy of the electrons is converted into a lattice vibration of the atoms, transiently heating the semiconductor to a high temperature and thus promoting the crystallization (activation) of the semiconductor.
However, in such a prior art impurity activation by a laser annealing as described above, a laser apparatus with a relatively large output power is required since efficiency in energy utilization is low, and therefore the manufacturing cost tends to be increased. Furthermore, according to such a method, it is not easy to carry out the activation of impurity with high reliability and to produce semiconductor devices with desirable characteristics. In particular, the production of semiconductor devices with desirable characteristics is difficult in the activation of p-type impurities in the case of SiC.